1. Field of Invention
The invention relates to a method for producing dehydrated vegetables capable of rapid reconstitution. More particularly, the invention is directed to a sequence of cooking, freezing and dehydration steps carried out under controlled conditions so as to produce a product having a porous interior and exterior surface.
2. Description of the Prior Art
Dehydration is one of the oldest methods for preserving food. Commercial production of dehydrated foods, however, is a development of the twentieth century. During the last forty years many procedures have been developed in an attempt to produce dehydrated products which upon reconstitution resemble fresh food in taste, texture, and appearance. More recently there has been a general concern for quick rehydrating products. Most of these efforts have resulted in unsatisfactory processes and products. A problem common to prior dehydration methods is a phenomenon referred to as case-hardening or the formation of a horny, vitreous material primarily on the surface of the food. It has been postulated that this may result from the collapse of the cellular structure of the vegetable which dehydrates into a dense mass of material of low rehydration characteristics.
Prior art methods for producing quick rehydrating products include soaking the material in solutions of salt or leavening agents prior to dehydration, subjecting food material to dehydration techniques which effect an expansion or puffing of the product and freeze-drying. U.S. Pat. No. 2,705,679, dehydrates potato dice using a fluidized bed dryer to form tan-colored pieces hollow in the center with the sides puffed out much as are the sides of a pillow. U.S. Pat. No. 3,338,724 discloses the importance of soaking potato pieces in a salt solution prior to such dehydration to produce puffed potato products having a density of 0.15 to 0.20 gm/cc. U.S. Pat. No. 3,438,792 freeze dries potatoes prior to finish drying in hot air to avoid case-hardening. U.S. Pat. No. 3,644,129 is based on the discovery that minimizing the to such combined freeze drying-hot air drying is effective in improving the rehydration characteristics of the dehydrated product. U.S. Pat. No. 3,573,070 discloses a process comprising freezing prior to combined freeze drying-hot air drying in an attempt to produce improved dehydrated products. U.S. Pat. No. 3,188,750 attempts to produce a dehydrated product possessing a high degree of biological integrity by first hot air drying raw material prior to freeze drying which is preferably followed by another hot air drying. U.S. Pat. No. 2,729,566 teaches that rapid freezing followed by a slow thawing at a temperature within the range of 28.degree. F. to 32.degree. F. for at least 15 minutes prior to hot air dehydration is critical and that potato pieces being processed should not reach a temperature higher than about 130.degree. F. during dehydration. U.S. Pat. No. 2,707,684, however, discloses that if potato pieces are rapidly frozen prior to dehydration, the final products will have a slow rehydration rate. U.S. Pat. No. 2,713,003 preconditions food products by freezing, throughout or superficially, prior to dehydrating. U.S. Pat. No. 2,278,472 also freezes food prior to dehydration. U.S. Pat. No. 3,359,123 is directed to rendering potatoes more amenable to freeze-thaw procedures by a controlled cooking procedure which avoids moisture pickup by the potato followed by dehydrating the product under such conditions so as to avoid any further gelatinization of the potato pieces, for example, by drying in air having a 20 to 40% relative humidity. G.B. Patent No. 1,084,714 dehydrates vegetables in a gas containing from about 5% to about 50% by weight of water vapor at a temperature from 194.degree. F. to 428.degree. F. U.S. Pat. No. 3,973,047 is directed to reducing the level of microorganisms in dehydrated vegetables by subjecting vegetables, partially dried to between 8 and 50% moisture, to air having dry bulb/wet bulb temperatures, ranging from 200.degree. F. dry bulb/180.degree. F. wet bulb to about 140.degree. F. dry bulb/120.degree. F. wet bulb, which are sufficiently high to kill bacteria without causing significant dehydration, prior to finish drying to a final moisture content of less than about 8%.
The foregoing disclosures are representative of the attempts made to overcome the shortcomings of dehydrated food products as compared to freshly prepared foodstuff. The food industry has had to rely on similar procedures to prepare dehydrated vegetables over the years. Recently, cooking and eating habits have been influenced by a number of factors which reduce the time allocated for food preparation in households as well as in eating establishments. This has caused a need for good nutritious foods which can be prepared quickly and easily. A number of frozen entree, side dish, and complete dinners, in addition to canned products, have been available in the marketplace which attempt to satisfy the consumer's need for convenient foods. Notwithstanding numerous efforts to develop industrially produced and commercially acceptable dehydrated food products, there is a limited number of dehydrated vegetable products on the market. Such vegetables are primarily used as flavoring in soups, stocks, casseroles, and the like. Moreover, dehydrated vegetables used in instant soups, i.e., having a reconstitution time of less than about 5-20 minutes, have been small in size in order to permit preparation within the prescribed time period. Normally the vegetable piece size is no larger than about 1/8 inch in cross-section. Typically, the dehydrated products have been reduced to a powder. Complaints about such products include that the dehydrated pieces reconstitute incompletely and are tough and chewy despite their small size. Larger vegetable pieces have only recently been used as ingredients in commercial mixes containing dehydrated vegetables, stock seasoning, and noodles. These mixes are used as starting materials for preparation of soup to which only water and meat need be added in the kitchen. Their recipe normally requires as long as 11/2 hours in preparation for consumption.